1. Field of the Invention
This invention relates to a large aperture ratio photographic lens which has a standard angle of view and yet in which the photographing near distance is shorter than that in ordinary lenses.
2. Description of the Prior Art
In most of conventional large aperture ratio lenses, aberration correction is effected with infinity photography as the standard and, as is known, the imaging performance is significantly deteriorated during short distance photography, and as the aperture ratio increases, various aberrations fluctuate greatly. In practical use, the photographing magnification during near distance photography has been of the order of 1/10 and, particularly, in the case of a large aperture ratio lens, it has been difficult to say that the performance during open photography is sufficient even at such degree of magnification. To prevent such deterioration of the imaging performance, various types of so-called floating systems for correcting aberrations in which partly different movements are effected within the lens system during short distance photography have been adopted instead of the conventional so-called whole axial movement system, whereby the fluctuations of various aberrations during a short distance photography condition can be reduced and the photographing distance can be made shorter than in the case of the whole axial movement system. However, some of these known floating systems have generally had complicated constructions and some of them have involved movement of the lens which is difficult to carry out for higher magnification photography. Even in some of them which are simple in construction, the deterioration of the image resulting from chromatic aberration has been severe and, particularly, in the case of a large aperture ratio, the photographing distance has been prevented from being shortened.